Fire-resistant functional fluid compositions

ABSTRACT

PRODUCTION OF FUNCTIONAL FLUIDS, PARTICULARLY AIRCRAFT HYDRAULIC FLUIDS, OF IMPROVED FIRE RESISTANCE, COMPRISING A FUNCTIONAL FLUID BASE STOCK, SUCH AAS A PHOSPHATE ESTER, E.G., TRI-N-BUTYL PHOSPHATE, OR MIXTURES OF SUCH BASE STOCKS, AND A SMALL AMMMOUNT OF A DISELENO ALKANE COMPOUND, E.G., 3,8-DISELENO-N-DECANE.

United States Patent C) 3,730,889 FIRE-RESISTANT FUNCTIONAL FLUID COMPDSITIONS Robert S. McCord, Pacific Palisades, Donald H. Nail, Los Angeles, and Martin B. Sheratte, Reseda, Calif., assignors to McDonnell Douglas Corporation, Santa Monica, Calif. No Drawing. Filed May 3, 1971, Ser. No. 139,869 Int. Cl. C09k 3/00 U.S. Cl. 252-78 26 Claims ABSTRACT OF THE DISCLOSURE Production of functional fluids, particularly aircraft hydraulic fluids, of improved fire resistance, comprising a functional fluid base stock, such as a phosphate ester, e.g., tri-n-butyl phosphate, or mixtures of such base stocks, and a small amount of a diseleno alkane compound, e.g., 3,8-diseleno-n-decane.

This invention relates to functional fluid compositions having improved fire resistance and is particularly directed to compositions comprising certain functional fluids and an additive amount suflicient to improve fire resistance, of certain selenium compounds.

Many different types of materials are employed as functional fluids and functional fluids are utilized in a wide variety of applications. Thus, such fluids have been utilized as electronic coolants, diffusion pump fluids, lubricants, damping fluid, power transmission and hydraulic fluids, heat transfer fluids and heat pump fluids. A particularly important application of such functional fluids has been their utilization as hydraulic fluids and lubricants in aircraft, requiring successful operation of such fluids over a wide temperature range, a particularly important and highly desirable property of such fluids being fire resistance.

Functional and hydraulic fluids employed in many industrial applications and particularly hydraulic fluids for aircraft must meet a number of important requirements. Thus, such hydraulic fluids particularly for aircraft use, should be operable over a wide temperature range, should have good stability at relatively high temperatures and preferably have lubricating characteristics. In addition to having the usual combination of properties making it a good lubricant or hydraulic fluid, such fluid should also have relatively low viscosity at extremely low temperatures and an adequately high viscosity at relatively high temperatures, and must have adequate stability at the high operating temperatures of use. Further, it is of importance that such fluids be compatible with and not adversely affect materials including metals and non-metals such as elastomeric seals of the system in which the fluid is employed. It is particularly important in aircraft hydraulic fluids and lubricants that such fluids have as high a fire resistance as possible to prevent ignition if such fluids are accidentally or as result of damage to the hydraulic system, sprayed onto or into contact with surfaces or materials of high temperature.

While many functional and hydraulic fluid compositions have been developed having most of the aforementioned required properties, many of these compositions do not have the requisite high fire resistance desired particularly for use of such functional fluid or hydraulic fluid compositions in modern high speed aircraft or in a hydraulic systern located near a high temperature jet-turbine power plant of a jet-turbine aircraft.

Thus, as an illustration, many functional and hydraulic fluids have an autoignition temperature ranging from about 450 to about 750 F. It is particularly desirable to increase the autoignition temperature of such functional and hydraulic fluids above 750" F., e.g., to the range of about 800 to about 1,000 F.

It has now been found in accordance with the present invention that the fire resistance, or autoignition temperature, of functional fluid or hydraulic fluid compositions, can be significantly improved by the addition to such compositions of a small amount of certain selenium compounds, in the form of certain diseleno alkanes, defined in greater detail hereinafter. The inclusion of such selenium-containing additives in functional and hydraulic fluid compositions generally does not adversely affect any of the above noted important characteristics of such fluids, particularly aircraft hydraulic fluids, including their desirable viscosity characteristics.

Another important feature is that certain recently developed hydraulic fluids for aircraft use have been designed particularly to have reduced density, but many of these low density fluids have inferior fire resistance to the higher density hydraulic fluids, and it has been found that the selenium additives of the invention when incorporated into such low density fluids substantially increase the fire resistance and reduce the flammability of these low density hydraulic fluids.

The use of dialkyl selenides as oxidation inhibitors for orthosilicate fluids is described in U.S. Pat. 3,118,841 to Moreton. In such patent the selenide, e.g., dilauryl selenide, is employed in combination with other oxidation inhibitors such as phenyl alpha naphthylamine. However, selenides which inhibit oxidation in liquids do not necessarily function to reduce flammability, or to increase autogenous ignition temperature of a fluid, and in such patent only orthosilicates are employed as the base stock. Further, many of the selenides are toxic, thermally unstable and/or insufliciently soluble at the working temperature. Certain selenides also tend to corrode metals. Moreover, in order to effectively reduce flammability, selenium compounds should also possess the property of decomposting in the plasma condition in flames to prevent or poison continuation of the flame.

It has been found that certain diseleno alkanes as defined below, not only function to substantially increase autogenous ignition (autoignition) temperature and reduce flammability of a wide variety of functional fluids and hydraulic fluids, but in addition have the advantageous properties of being thermally stable, free from toxicity, relatively free from corrosion, and have suf ficient solubility in most functional and hydraulic fluids to effectively function as flame inhibitors. In addition, the diseleno alkanes employed according to the invention have no adverse effect on low temperature viscosity of the functional fluids, particularly when employed as hydraulic fluids in aircraft, do not adversely affect the thermal stability of the fluid, and are of relatively low cost.

Effective selenium compounds, that is, diseleno alkanes, for use as additives in functional hydraulic fluids to reduce flammability and increase autoignition temperature of the fluid, according to the invention have the formula:

where R and R are each alkyl, either straight chain or branched chain, of from about 1 to about 5 carbon atoms, and where R and R can be the same or different, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, namyl and isoamyl, and n. is an integer of from 3 to 6. Where R and R each contain more than 5 carbon atoms and/ or n is an integer greater than 6, solubility of the additives in the functional fluid is generally insufficient.

Specific examples of diseleno alkanes according to the invention are the following:

The preferred diseleno alkane additive which has been found particularly effective according to the invention, 1s compound 3 above, namely, 3,8-diseleno-n-decane. Mixtures of different diseleno alkanes can also be employed, e.g., a mixture of compounds 2 and 3 above.

The following base stocks are illustrative of typical base stocks that can be utilized in preparing the functional fluid compositions of the present invention, and the instant invention can be practiced utilizing the various modifications of the base stocks which are set forth below:

Preferably functional fluid base stocks are employed which are selected from the group consisting of phosphorus esters, amides of an acid of phosphorus, diand tricarboxylic acid esters, and petroleum hydrocarbons.

Phosphorus esters which can be employed according to the invention have the general formula:

where s, m and n can be or 1, and not more than two of s, m, and n can be 0, where R R and R each can be aryl such as phenyl and naphthyl, alkaryl such as cresyl, xylyl, ethyl phenyl, propyl phenyl, isopropyl phenyl, and the like, said aryl and alkaryl radicals preferably containing from 6 to about 8 carbon atoms, alkyl, both straight chain and branched chain of from about 3 to about 10 carbon atoms such as n-propyl, n-butyl, n-amyl, n-hexyl, isopropyl, isobutyl, and the like, and alkoxyalkyl having from about 3 to about 8 carbon atoms such as methoxy methyl, methoxy ethyl, ethoxy ethyl, methoxy propyl, and the like.

The corresponding phosphonates can also be employed, where one of s, m and n is 0, and the corresponding phosphinates where two of s, m and n are 0.

Preferred phosphorus esters are the dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates.

Examples of such phosphate esters are the dialkyl aryl phosphates in which the alkyl groups are either straight chain or branched chain and contain from about 3 to about 10 carbon atoms, such as n-propyl, n-butyl, n-amyl, n-hexyl, isopropyl, isobutyl, isoamyl, and the aryl radicals have from 6 to 8 carbon atoms and can be phenyl, cresyl or xylyl, particularly dialkyl phenyl phosphates including dibutyl phenyl phosphate, butyl amyl phenyl phosphate, butyl hexyl phenyl phosphate, butyl heptyl phenyl phosphate, butyl octyl phenyl phosphate, diamyl phenyl phosphate, amyl hexyl phenyl phosphate, amyl heptyl phenyl phosphate, and dihexyl phenyl phosphate.

Examples of triaryl phosphates to which the diseleno alkanes of the invention can be added are those in which the aryl radicals of such phosphates have from 6 to 8 carbon atoms, that is, may be phenyl, cresyl or xylyl, and in which the total number of carbon atoms in all three of the aryl radicals is from 19 to 24, that is, in which the three radicals include at least one cresyl or xylyl radical.

Examples of such phosphates include tricresyl, trixylyl, phenyl dicresyl, and cresyl diphenyl phosphates.

Examples of trialkyl phosphates employed according to the invention include phosphates having alkyl groups which are either straight chain or branched chain with from about 3 to about 10 carbon atoms, such as n-propyl, n-butyl, n-amyl and n-hexyl, particularly tri-n-butyl phosphate, tri(2-ethyl hexyl) phosphate and triisononyl phosphate, the straight chain alkyl groups preferably containing from 4 to 6 carbon atoms.

Examples of alkyl diaryl phosphates which can be employed to produce the invention compositions include those in which the aryl radicals of such phosphates may have from 6 to 8 carbon atoms and may be phenyl, cresyl or xylyl, and the alkyl radical may have from about 3 to about 10 carbon atoms, examples of which are given above. Examples of the alkyl diaryl phosphates include butyl diphenyl, amyl diphenyl, hexyl diphenyl, heptyl diphenyl, octyl diphenyl, 6-methyl heptyl diphenyl, 2-ethylhexyl diphenyl, butyl phenyl cresyl, amyl phenyl xylyl, and butyl dicresyl phosphates.

Functional fluid base stocks according to the invention also include phosphonate and phosphinate esters having alkyl and aryl groups corresponding to those defined above with respect to the phosphate esters.

Examples of phosphinate esters to which the invention principles are applicable include phenyl-di-n-propyl phosphinate, phenyl-di-n-butyl phosphinate, phenyl-di-npentyl phosphinate, p-methoxyphenyl-di-n-butyl phosphinate, tert-butylphenyl-di-n-butyl phosphinate. Examples of phosphonate esters to which the invention is applicable include aliphatic phosphonates such as an alkyl alkenyl phosphonate, e.g., dioctyl isooctene phosphonate, an alkyl alkane phosphonate such as di-n-butyl n-octane phosphonate, di-isooctyl pentane phosphonate, and dimethyl decane phosphonate, a mixed alkyl aryl phosphonate, for example, di-octyl phenyl phosphonate, di(n-amyl) phenyl phosphonate, di(n-butyl) phenyl phosphonate, phenyl butyl hexane phosphonate and butyl bis-benzene phosphonate.

Another class of phosphorus-containing compounds in which the diseleno alkanes of the invention can be employed as additives are the amides of acids of phosphorus, e.g., amido phosphates, including the mono-, diand triamides of an acid of phosphorus, an example of which is phenyl N methyl N n butyl N-methyl-N'-n-butyl phosphoro-diamidate. Additional examples are m-cresyl-p-cresyl-N,N-dimethylphosphoroamidate, di-m-cresyl-N,N-dimethylphosphoroamidate, di-p-cresyl-N,N-dimethyl-phosphoroamidate, phenyl-N,N-dimethyl-N',N'-dimethylphosphorodiamidate, N-methyl-N-butyl-N,N"-tetrarnethylphosphorotriamidate, N,N'-di-n-propyl-N"-dimethylphosphorotriamidate.

Another class of functional fluid base stocks whose autoignition temperature can be improved by incorporation of the diseleno alkanes of the invention are the diand tricarboxylic acid esters, particularly the dicarboxylic acid esters. Preferred types of the latter compounds are the alkyl diesters of adipic and sebacic acid, that is the diester adipates and sebacates. Such esters can contain alkyl groups, either straight chain or branched chain, containing from about 4 to about 12 carbon atoms including butyl, isobutyl, amyl, pentyl, hexyl, isohexyl, nonyl, decyl and isodecyl groups. Specific examples of these base stocks are dihexyl, di-Z-ethylhexyl, dioctyl, dinonyl, didecyl and diisodecyl adipate, and the corresponding sebacates. Also, the diesters of the dicarboxylic aromatic acids, particularly the diesters of phthalic acid, that is the phthalate diesters, can be employed as base stocks. The diesters of such acids can contain alkyl groups of from 4 to 12 carbon atoms, examples of which are given above with respect to the diesters of the dicarboxylic aliphatic acids,

adipic and sebacic acid. Illustrative examples of the diester phthalates which can be employed are di-n-butyl phthalate, dihexyl phthalate, dioctyl phthalate, dinonyl phthalate, didecyl phthalate, and diisodecyl phthalate.

There can also be employed as functional fluid base stocks according to the invention the esters of tricarboxylic acids, particularly the aromatic tricarboxylic acids such as trimellitic acid. The triesters of such acids can contain alkyl groups of from 4 to 12 carbon atoms, illustrative examples of which are noted above with respect to the dialkyl esters of phthalic acid, specific examples of trimellitate triesters including tri-butyl, tri-hexyl, trioctyl, tri-isooctyl, tri-nonyl, tri-decyl and tri-isodecyl trimellitate.

There can also be employed as functional fluid base stocks to which the diseleno alkanes are added according to the invention, petroleum hydrocarbons, which can contain carbon chains of from C to about C carbon atoms. A typical example of such a petroleum hydrocarbon is the red petroleum hydrocarbon liquid according to military specification MIL-H-5606B, understood to contain carbon chains of about C to about C carbon atoms, generally employed as a hydraulic fluid in military aircraft.

It is also contemplated within the scope of the present invention that mixtures of individual functional or hydraulic fluid components are included to form a single base stock. Thus, for example, blends of esters of an acid of phosphorus can be employed, e.g., a blend of tri-nbutyl phosphate and tricresyl phosphate, blends of an ester of an acid of phosphorus and a dicarboxylic acid diester such as the aliphatic diesters of adipic, sebacic or phthalic acid, e.g., a mixture of tri-n-butyl phosphate and di-isodecyl adipate and/or di-isodecyl phthalate, or a combination or blend of dicarboxylic acid diesters and/ or tricarboxylic acid triesters can be employed, such as a blend of di-isodecyl adipate and di-isodecyl phthalate.

Thus, there can be employed as functional fluid base stocks a blend or mixture of a phosphorus ester such as a phosphate and an alkyl diester of phthalic acid, with or without an alkyl diester of adipic acid and/or of sebacic acid, wherein said alkyl groups contain from about 4 to about 12 carbon atoms as described and claimed in the copending application, Functional Fluid Compositions, M. B. Sheratte, Ser. No. 129,270, filed Mar. 29', 1971. In addition, functional fluid base stocks can be utilized comprising a blend or mixture of a phosphorus ester such as a phosphate and an alkyl diester of adipic acid and/or of sebacic acid, as defined above, and as described and claimed in the copending application, Functional Fluids, M. B. Sheratte, Ser. No. 129,269, filed Mar. 29, 1971.

The functional or hydraulic fluid base stocks employed and described above, can also contain other additives such as viscosity index improvers, in a small amount ranging from to about generally about 2 to about 10%, by weight of the composition. Examples of the latter are polyalkyl acrylates and methacrylates, the polyalkyl methacrylates generally being preferred, and in which the alkyl groups may contain from about 4 to about 12 carbon atoms, either straight or branched chain, and having an average molecular Weight ranging from about 6,000 to about 15,000. Specific examples of such viscosity index improvers are polybutyl methacrylate and poly n-hexyl acrylate, having an average molecular weight between about 6,000 and about 12,000. Other additives such as corrosion inhibitors, stabilizers, metal deactivators, and the like, can also be employed.

For greatest effectiveness in substantially reducing the flammability, and for correspondingly substantially increasing the autoignition temperature of the above functional fluid base stocks according to the invention, it is usually desirable to employ only a small amount of the diseleno alkane in the functional or hydraulic fluid base stock. Generally, there can be employed as little as about 0.15% and up to about 5% of the diseleno alkane additive of the invention, preferably from about 0.5 to about 2% of such selenide, in the functional fluid base stock, based on the weight of the composition. It has been found that an optimum amount of such selenide additive ranges from about 0.8 to about 2% by weight of the composition.

The diseleno alkanes employed according to the invention are prepared generally by production of sodium alkyl selenide, RSeNa, having the desired number of carbon atoms in the alkyl chain, that is, when R corresponds to R or R of the general formula for the diseleno alkanes noted above, and reacting said sodium alkyl selenide with a dibromo alkane, BrC H Br, where n is an integer of from 3 to 6, in a ratio of about 2 mols of the sodium alkyl selenide to 1 mol of the dibromo alkane. Mixtures of different dibromo alkanes can be employed. If desired, about 1 mol of each of two ditferent sodium alkyl selenides in which R is a different alkyl group, can be reacted with 1 mol of the dibromo alkane.

The following is an example of preparation of a preferred diseleno alkane additive according to the invention, such example being simply exemplary of the preparation generally of the diseleno alkanes employed as additive according to the invention:

EXAMPLE 1 Preparation of 3,8-di'seleno-n-decane A 500 ml. flask was equipped with a stirrer, thermom- I eter, liquid addition funnel, powder addition funnel and a Dewar condenser. Selenium (7.9 g., 0.1 mole) was placed in the powder addition funnel, and the apparatus was flushed with nitrogen. Liquid ammonia (approx. 200 ml.) was condensed into the flask, which was immersed in a Dry Ice-iso-propyl alcohol cooling bath. Sodium (2.3 g., 0.1 mole) was dissolved in the ammonia, and then the selenium was added to the solution. The reaction of selenium with sodium is exothermic and should be done with care. When about half the selenium had been added, the deep blue color of the sodium was suddenly discharged and replaced by a creamy precipitate. Further addition of selenium caused this precipitate to dissolve to yield a deep apple green solution of sodium diselenide.

Ethyl bromide (10.9 g., 0.1 mole) was then placed in the liquid addition funnel and added slowly to the sodium diselenide. solution. When the exotherm from this reaction had abated, the mixture was stirred at 40 C. for 2 hours. At the end of this time, the solution was colorless with a white precipitate of sodium bromide with diethyl diselenide in solution. Sodium was added to this solution piece by piece until the deep blue color once again persisted, forming sodium ethyl selenide. Approximately 2.5 g. (0.11 mole) of sodium was required for this purpose.

1,4-dibromobutane (20 g., 0.2 mole) was then placed in the liquid addition funnel and added slowly to the solution of sodium ethyl selenide. When the resulting exothermic reaction had subsided, the mixture was again stirred at 40 C. for two hours, when it had again become colorless. Approximately ml. ether was added to the reaction mixture and the ammonia was allowed to evaporate overnight.

The ether suspension was then Washed free of sodium salts, dried over sodium sulphate and fractionally distilled under vacuum. The product, which was obtained in 60% yield, had a boiling point of C. at 300 microns pressure.

Analysis.--Calcd. for C H Se Se, 58.1%. Found: Se, 61.9%.

The following are examples illustrating practice of the invention by incorporation of diseleno alkane additives according to the invention into functional fluid base stocks. In the examples below the term AIT means autoignition temperature, the autoignition temperature of the functional fluid compositions of the invention according to the examples below being determined in accordance with standard method of test for autoignition temperature in accordance with ASTM D 2155 procedure. All percentages are in terms of percent by weight of the functional fluid composition.

EXAMPLE 2 To aliquot portions of tri-n-butyl phosphate, designated Fluid A in the table below, is added varying minor amounts of 3,8 diseleno-n-decane, and the autoignition temperature of the various aliquot portions of the resulting fluid compositions, and of a control of Fluid A with no such selenide, is obtained.

The results of such tests are noted in the table below:

TAB LE Additive concentration (percent) AIT Fluid Additive A 3, 8-diselcuo -11-decane EXAMPLE 3 The procedure of Example 2 is repeated except employing in place of Fluid A in Example 2, a functional fluid blend comprising about 80% tri-n-butyl phosphate, about 11% tricresyl phosphate, and a small amount of polybutyl methacrylate viscosity index improver.

Results comparable to those of Example 2 are obtained, that is, the addition of the diseleno decane in varying proportions ranging from 0.25 to about 2.0% to the above functional fluid blend substantially increases AIT over the AIT of 740 F. for the functional fluid blend control in the absence of the diseleno decane additive, to values between about 850 F. and about 950 F., and the AIT of the functional fluid blend increases with increasing amount of the diseleno decane additive incorporated in the functional fluid blend.

EXAMPLE 4 The procedure of Example 2 is repeated employing each of the respective diseleno alkane additive compounds (1), (2) and (4) above, each such additive being employed in amounts ranging from 0.25 to 2.0% by weight in respective portions of the fluid composition.

For each of the diseleno alkane additive compounds (I), (2) and (4) incorporated in the tri-n-butyl phosphate Fluid A, AIT is substantially increased from the AIT of 730 F. for the control, in the absence of any diseleno alkane, to an AIT ranging from about 850 F. to about 950 F., with AIT increasing as the amount of diseleno alkane in each case is increased up to the 2.0% level.

EXAMPLE 5 The procedure of Example 2 is repeated, employing in place of Fluid A of Example 2, a functional fluid blend comprising 70% di-isodecyl adipate and 30% tri-n-butyl phosphate.

Results similar to those of Example 2 are obtained.

EXAMPLE 6 To a blend of a functional fluid containing about 70% di-isodecyl adipate and 30% tri-n-butyl phosphate are respectively added the diseleno alkane additive compounds (3), (6) and (9) above, each in amounts respectively of 0.5, 1.0 and 1.8%, by weight, to respective portions of the functional fluid blend.

For each of the diseleno additives (3), (6) and (9) added to the functional fluid blend of this example, AIT is substantially increased in the range of about 800 to 950 F., well above the less than 700 P. value for the control, in the absence of any diseleno alkane additive, and in each case for each of such diseleno alkane additives, the AIT increases with increasing amount of additive incorporated, up to the 1.8% level.

EXAMPLE 7 The procedure of Example 2 is repeated employing 3,8- diseleno-n-decane in each of the following functional fluids, in each fluid varying the proportion of such diseleno decane additive in the amounts noted in Example 2.

(I) A red petroleum hydrocarbon liquid containing hydrocarbon chains ranging from C to C (MIL-IL- 5606B).

(II) A blend of a functional fluid containing 50% diisodecyl adipate, 30% tri-n-butyl phosphate and 20% dibutyl phenyl phosphate.

(III) A blend of a functional fluid containing 50% diisodecyl adipate, 40% tri-n-butyl phosphate and 10% tri-isodecyl-tri-mellitate.

(IV) A blend of a functional fluid containing 39% trin-butyl phosphate, 47% di-isodecyl adipate and 10% diisodecyl phthalate.

For each of the functional fluids (I), (II), (III) and (IV) above, incorporation of the diseleno decane additive substantially increases AIT from that of the control, in the absence of any diseleno alkane additive, the AIT increasing in each case with increasing amount of diseleno decane additive incorporated, up to the 2.0% level, the incorporation of such additive in the above noted fluids '(II), (III) and (IV) particularly increasing the AIT of such fluids from the 600 to 700 F. range to the 800 to 900 F. range.

EXAMPLE 8 The procedure of Example 2 is repeated, employing in place of Fluid A of Example 2, phenyl N-methyl-N-nbutyl-N-methyl-N'-n-butyl phosphorodiamidate.

Results comparable to those of Example 2 are obtained.

In each of the Examples 2 to 8 above, a substantial improvement in autoignition temperature, and corresponding reduction in flammability is obtained, by incorporating the diseleno alkanes of the invention into the various functional fluids and blends thereof set forth in the examples, and such reduction in flammability is obtained without reducing the high temperature thermal stability of the functional fluid and without any increase in low temperature viscosity of the fluid, employing the selenium compounds of the invention having relatively good solubility in such fluids and high effectiveness therein, and which are relatively free from toxicity.

From the foregoing, it is seen that the invention provides novel functional fluid compositions containing certain organo-selenium compounds which function efficiently as flame retardants or flame inhibitors in such fluids.

While we have described particular embodiments of our invention for purposes of illustration, it will be understood that various changes and modifications within the spirit of the invention can be made, and the invention is not to be taken as limited except by the scope of the appended claims.

We claim:

1. A functional fluid composition consisting essentially of a major portion of a functional fluid base stock selected from the group consisting of phosphorus esters, amides of an acid of phosphorus, diand tricarboxylic acid esters,

and petroleum hydrocarbons containing carbon chains of from C to about C carbon atoms; and about 0.15 to about 5% by weight of said composition of a diseleno alkane having the formula:

where R, and R are each alkyl of from 1 to about 5 carbon atoms, and n is an integer of from 3 to 6.

2. A composition as defined as defined in claim 1, said diseleno alkane being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

3. A composition as defined in claim 1, wherein said diseleno alkane is 3,8-diseleno-n-decane.

4. A composition as defined in claim 2, wherein said diseleno alkane is 3,8-diseleno-n-decane.

5. A composition as defined in claim- 1, wherein said base stock is a phosphorus ester having the general formula:

where s, m and n are each an integer of to 1, and not more than two of s, m and n are 0, R R and R are each a member selected from the group consisting of aryl, alkaryl, alkyl of from about 3 to about 10 carbon atoms, and alkoxyalkyl having from about 3 to about 8 carbon atoms.

6. A composition as defined in claim 1, said base stock comprising a petroleum hyrocarbon containing carbon chains of from C to about C and said diseleno alkane is 3,8-diseleno-n-decane.

7. A composition as defined in claim 1, said base stock comprising a petroleum hydrocarbon containing carbon chains of from about C to about C said diseleno alkane is 3,8-diseleno-n-decane, said diseleno alkane being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

8. A functional fluid composition consisting essentially of a major portion of a functional fluid base stock, said base stock comprising a phosphate ester having the general formula:

where R R and R are each a member selected from the group consisting of aryl, alkaryl, alkyl of from about 3 to about 10 carbon atoms, and alkoxyalkyl having from about 3 to about 8 carbon atoms, and about 0.15 to about by weight of said composition of a compound having the formula where R and R are each alkyl of from about 1 to about 5 carbon atoms, and n is an integer of from 3 to 6.

9. A composition as defined in claim 8, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates.

10. A composition as defined in claim 8, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, said diseleno alkane being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

11. A composition as defined in claim 8, wherein said base stock comprises a mixture of a phosphate ester se- 10 lected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and a dicarboxylic acid ester.

12. A composition as defined in claim 11, wherein said dicarboxylic acid ester is selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

13. A composition as defined in claim 11, wherein said dicarboxylic acid ester is an alkyl diester of phthalic acid containing alkyl groups of from about 4 to about 12 carbon atoms.

14. A composition as defined in claim 13, wherein said mixture includes a dicarboxylic acid ester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

15. A composition as defined in claim 8, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and said diseleno alkane is 3,8-diselenon-decane.

16. A composition as defined in claim 8, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and said diseleno alkane is 3,8-diselenon-decane, said diseleno alkane being present in an amount ranging from about 0.5 to about 2% by Weight of said composition.

17. A composition as defined in claim 8, wherein said base stock comprises a mixture of a phosphate ester se lected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates and a dicarboxylic acid diester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms, and said diseleno alkane is 3,8-diseleno-n-decane.

18. A composition as defined in claim 8, said base stock comprising a mixture of a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl, and alkyl diaryl phosphates, and an alkyl diester of phthalic acid containing alkyl groups of from about 4 to about 12 carbon atoms, and said diseleno alkane is 3,8- diseleno-n-decane.

19. A composition as defined in claim 18, wherein said mixture includes a dicarboxylic acid ester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

20. A composition as defined in claim 8, said base stock comprising a member selected from the group consisting of di-n-butyl phenyl phosphate, tri-n-butyl phosphate and tricresyl phosphate, and mixtures thereof, and said diseleno alkane is 3,8-diseleno-n-decane.

21. A composition as defined in claim 20, said base stock comprising a mixture of tri-n-butyl phosphate and tricresyl phosphate.

22. A composition as defined in claim 20, said base stock including a member selected from the group consisting of diisodecyl adipate and diisodecyl phthalate, and mixtures thereof.

23. A composition as defined in claim 20, said base stock including a mixture of di-isodecyl phthalate and diisodecyl adipate.

24. A composition as defined in claim 20, said base stock being a mixture of tri-n-butyl phosphate, diisodecyl adipate and diisodecyl phthalate.

25. A composition as defined in claim 8, said base stock comprising a member selected from the group consisting of di-n-butyl phenyl phosphate, tri-n-butyl phosphate and tricresyl phosphate, and mixtures thereof, and said diseleno alkane is 3,8-diseleno-n-decane, said diseleno alkane being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

11 12 26. A composition as defined in claim 22, said base 3,074,889 1/1963 Attwood 25278 stock comprising a mixture of tri-n-butyl phosphate, di- 3,280,031 10/1966 Brennan et a1 25278 X butyl phenyl phosphate and diisodecyl adipate.

MAYER WEINBLA'IT, Primary Examiner References cited 5 H. A. PITLICK, Assistant Examiner UNITED STATES PATENTS 2,473,510 6/1949 Denison et a1 2s2 4s 2,792,346 5/1957 Undert 25246.7 2s2 4s, 46.7, 48.6; 260-607 R, 666.5, 989 

